(1) Field of the Invention
The present invention relates to a method and apparatus for detecting reference rotational angles in a multiple-cylinder internal combustion engine. More particularly, the present invention relates to a method and apparatus for detecting the reference rotational angles, by which it is possible to judge that a specific cylinder is at a specific stroke.
(2) Description of the Related Art
A crank angle sensor has heretofore been used for making various controls, for example, the control of the ignition timing, in an internal combustion engine.
There are known various systems for making various controls for the engine, for example, the control of the ignition timing, in cylinders by using crank angle sensors, and recently, there is often adopted a system in which a crank angle sensor having only a function of outputting a reference pulse signal at a specific crank angle (a reference rotational angle) position during a specific stroke of each cylinder synchronously with the revolution of the engine is used and the ignition timing is computed based on the detected reference pulse signal by a microcomputer (see Japanese Utility Model Application No. 62-133304).
The reason for adoption of this system is that it is not necessary to impart a function of generating a unit signal at every crank angle of 1 to 2 to the crank angle sensor and the cost can be advantageously reduced.
However, in the case where an electric current for ignition is electronically applied to each cylinder without using a mechanical distributer or in the case where not only the ignition timing control system but also a system for injecting a fuel to respective cylinders independently is adopted, it is necessary to obtain not only a reference pulse signal but also a signal for judging that a specific cylinder is at a specific stroke (hereinafter referred to as "independent judgement for each cylinder") and therefore, at least two systems become necessary for a group comprising a pickup device and a signal-processing circuit. Accordingly, reduction of the cost is limited.